In a 3rd Generation Partnership Project (3rd Generation Partnership Project, 3GPP) Long Term Evolution (Long Term Evolution, LTE) or LTE-advanced (LTE-advanced, LTE-A) system, an orthogonal frequency division multiple access (Orthogonal Frequency Division Multiple Access, OFDMA) mode is generally used as a downlink multiple access mode. Downlink resources of the system are divided into OFDM symbols in terms of time, and are divided into subcarriers in terms of frequencies. A subcarrier in an OFDM symbol is referred to as a resource element (Resource Element, RE). In LTE release (Release) 8/9/10, a resource block (Resource Block, RB) is defined. One RB includes 12 subcarriers in a frequency domain, and is one timeslot in a time domain, that is, it includes 7 or 6 OFDM symbols. Therefore, one RB includes 84 or 72 REs. In same subcarriers in a subframe, a pair of RBs of two timeslots is referred to as a resource block pair (RB pair), namely, a PRB.
In an LTE system of LTE release 10 or earlier, a physical downlink control channel (Physical Downlink Control Channel, PDCCH) and a physical downlink shared channel (Physical Downlink Shared Channel, PDSCH) are time division multiplexed in a subframe. The PDCCH is carried in the first n OFDM symbols in a subframe, where n may be any one of 1, 2, 3, and 4. In the frequency domain, and the PDCCH is distributed over an entire system bandwidth after interleaving processing. The PDSCH scheduled by the PDCCH is mapped starting from an (n+1)th OFDM symbol in the subframe. A complete PDCCH includes one or several control channel elements (Control Channel Element, CCE). One CCE includes 9 resource element groups (Resource Element Group, REG). One REG occupies 4 REs. In LTE release 8/9/10, one PDCCH may include 1, 2, 4, or 8 CCEs, that is, corresponding aggregation levels are 1, 2, 4, and 8 respectively, and quantities of PDCCH candidates on the aggregation levels are 6, 6, 2, and 2 respectively. When a base station transmits a PDCCH, it needs to determine CCE resources to which PDCCH candidates on the different aggregation levels are mapped.
In an LTE system later than release 10, for example, in LTE release 11, due to introduction of technologies such as multi-user multiple-input multiple-output (Multiple-Input Multiple-Output, MIMO) and coordinated multi-point (Coordinated Multi-Points, CoMP) transmission, a capacity of a control channel is limited. Therefore, a PDCCH transmitted based on a MIMO precoding mode is introduced. This PDCCH may be demodulated based on a UE-specific demodulation reference signal (Demodulation Reference Signals, DMRS), and is referred to as an enhanced PDCCH (Enhanced-PDCCH, E-PDCCH). The E-PDCCH is not in a control region of the first n OFDM symbols in a subframe, but in a region for transmitting downlink data in the subframe. In addition, the E-PDCCH and PDSCH are multiplexed in the data region of the subframe in a frequency division multiplexing (Frequency Division Multiplexing, FDM) mode. As may be seen from the foregoing description, time-frequency resources occupied by the E-PDCCH are different from those occupied by the PDCCH in the prior art, and a PDCCH transmission mode cannot be directly used to transmit the E-PDCCH. Therefore, a transmission problem of the E-PDCCH needs to be solved.